History

T-O-R-U-S 72a25d05bf Use implicit capture syntax in format_args This updates the standard library's documentation to use the new syntax. The documentation is worthwhile to update as it should be more idiomatic (particularly for features like this, which are nice for users to get acquainted with). The general codebase is likely more hassle than benefit to update: it'll hurt git blame, and generally updates can be done by folks updating the code if (and when) that makes things more readable with the new format. A few places in the compiler and library code are updated (mostly just due to already having been done when this commit was first authored).		2022-03-10 10:23:40 -05:00
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Cargo.toml	Sync rust-lang/portable-simd@03f6fbb21e	2022-01-27 11:23:40 -08:00
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README.md

README.md

The Rust standard library's portable SIMD API

Code repository for the Portable SIMD Project Group. Please refer to CONTRIBUTING.md for our contributing guidelines.

The docs for this crate are published from the main branch. You can read them here.

If you have questions about SIMD, we have begun writing a guide. We can also be found on Zulip.

If you are interested in support for a specific architecture, you may want stdarch instead.

Hello World

Now we're gonna dip our toes into this world with a small SIMD "Hello, World!" example. Make sure your compiler is up to date and using nightly. We can do that by running

rustup update -- nightly

or by setting up rustup default nightly or else with cargo +nightly {build,test,run}. After updating, run

cargo new hellosimd

to create a new crate. Edit hellosimd/Cargo.toml to be

[package]
name = "hellosimd"
version = "0.1.0"
edition = "2018"
[dependencies]
core_simd = { git = "https://github.com/rust-lang/portable-simd" }

and finally write this in src/main.rs:

use core_simd::*;
fn main() {
    let a = f32x4::splat(10.0);
    let b = f32x4::from_array([1.0, 2.0, 3.0, 4.0]);
    println!("{:?}", a + b);
}

Explanation: We import all the bindings from the crate with the first line. Then, we construct our SIMD vectors with methods like splat or from_array. Finally, we can use operators on them like + and the appropriate SIMD instructions will be carried out. When we run cargo run you should get [11.0, 12.0, 13.0, 14.0].

Code Organization

Currently the crate is organized so that each element type is a file, and then the 64-bit, 128-bit, 256-bit, and 512-bit vectors using those types are contained in said file.

All types are then exported as a single, flat module.

Depending on the size of the primitive type, the number of lanes the vector will have varies. For example, 128-bit vectors have four f32 lanes and two f64 lanes.

The supported element types are as follows:

Floating Point: f32, f64
Signed Integers: i8, i16, i32, i64, i128, isize
Unsigned Integers: u8, u16, u32, u64, u128, usize
Masks: mask8, mask16, mask32, mask64, mask128, masksize

Floating point, signed integers, and unsigned integers are the primitive types you're already used to. The mask types are "truthy" values, but they use the number of bits in their name instead of just 1 bit like a normal bool uses.